“I observe that when we mention any great number, such as a thousand, the mind has generally no adequate idea of it, but only a power of producing such an idea by its adequate idea of the decimals, under which the number is comprehended.” Stanislas Dehaene, The Number Sense: how the mind creates mathematics (Oxford 2d ed. 2011) at 79, quoted David Hume, A Treatise of Human Nature, and set me to agreeing.
We can’t grasp 10,000 very well (one quarter of the attendees at Citifield?) let alone one million dollars. Evolutionary psychologists would say that homo sapiens on the great plains of Africa did not need to count above a few score, so our brains never evolved to cope with numbers a thousand or more times bigger. Perhaps decimals help some people. Probably, though, most of us toss around large numbers – GDPs in the trillions, revenues in the billions, fees in the millions – but aren’t really comfortable with the magnitude of numbers at those scales.